The present invention relates to an acoustically dampened striker bar for use in impact printers and particularly relates to a novel assembly and method of assembling a striker bar body and print frame mounting members one to the other to afford acoustical dampening.
Impact printers, particularly high-speed impact printers, use a variety of means to reduce the acoustic noise generated by the printhead impacting the striker bar or platen through the ribbon and paper. For example, a striker bar formed of an elastomeric material to absorb vibration and soften impact has been used. However, print speed is limited because of the long dwell times of the print head against the ribbon and paper caused by the viscous dampening effect of the elastomer. Often, the rigid striker bar is shock-mounted to the printer frame through an elastomeric dampening material at the mounting points. This type of mounting, however, increases the likelihood of alignment problems and virtually guarantees that striker bars must be adjusted to maintain parallelism between the striker bar and print carriage rails of the printer. Moreover, most elastomers take a compression set and, consequently, field alignment problems, as well as acoustical problems, arise. The striker bar may also be hard-mounted to the printer frame, with the frame being isolated from the enclosure and the table top on which the printer sits. However, the dampening in this arrangement is less effective the greater the distance the dampening material is from the source of the noise and, consequently, more dampening material will be needed to obtain the same acoustic levels.
According to the present invention, there is provided an acoustically dampened striker bar that enables direct placement of the solid striker bar in the printer with no adjustment, enables reduction in acoustic noise levels to very low levels, has substantially insignificant motion while dampening thereby having little or no effect on print quality and is so constructed that the molded elastomeric material thereof has stresses which inherently cancel one another, virtually eliminating shrinkage of the material in the front-to-back, i.e., acoustical dampening, direction. Importantly, the striker bar of the present invention includes a rigid striker or impact surface and yet is directly dampened to the printer frame. The installation may be obtained without adjustment to compensate for dampening layers in the striker bar, i.e., no adjustment for parallelism of the striker bar relative to the carriage rails is required.
To accomplish the foregoing, the striker bar assembly of the present invention includes a rigid striker bar body, preferably formed of rigid steel or cast iron, a pair of end pieces or members for the striker bar body, preferably formed by a powdered metal process, and an elastomeric dampening material for interposition in a unique and novel manner between the end pieces and the striker bar body. In a preferred embodiment of the present invention, the end mounting members are generally T-shaped, with the cross part of the T shape having tapped mounting holes for mounting to the printer frame. The opposite ends of the striker bar body are recessed to form a generally U-shaped opening which may be machined or cast. The striker bar body has a front striker or impact surface and the recessed or slotted ends of the striker bar body open through the top and bottom surfaces thereof to form generally U-shaped ends. The striker bar body also has a greater depth than height. The distance between the wall surfaces defining each recess in the striker bar body is substantially larger than the width of the leg or projecting element of each end member. Thus, when the end members are assembled onto the striker bar by inserting the elements into the recesses, the elements and striker bar body are spaced one from the other to provide a uniform gap therebetween. That is, when the element of the end member is inserted into the recess, the wall surfaces defining the recess in the plane of the striker bar body behind the impact surface are spaced equally from the wall surfaces of the element.
These gaps are filled with dampening material. The dampening material is preferably an elastomer, for example, santoprene, nitrile, PVC, urethane or double-sided adhesive foam tapes and the like. It will be appreciated that the dampening material can be formed in the striker bar assembly by molding, casting or in place, dependent on the type of material used. If extruded materials are used, they are cut to size and adhesively secured in place with pressure. For molding, for example, injection-molding of santoprene, PVC or urethanes or transfer-molding with nitrile or SBR, the geometry of the parts becomes important to prevent flooding of the dampening material during molding. Thus, the end pieces are provided with projecting crush ribs which extend beyond the surfaces of the striker bar. During molding, these ribs are crushed to prevent flooding of the dampening material.
In a preferred embodiment according to the present invention, there is provided an acoustically dampened striker bar assembly for an impact printer comprising an elongated striker bar having wall surfaces defining a recess in each of its opposite ends, a member at each of the opposite ends of the striker bar for mounting the bar in the printer, each member having an element received in the recess in the corresponding end of the striker bar, the element having wallsurfaces spaced from and out of contact with the wall surfaces of the striker bar recess and an elastomeric dampening material disposed between the wall surfaces of the elements and the recesses, respectively.
In a further preferred embodiment according to the present invention, there is provided an acoustically dampened striker bar assembly for an impact printer comprising an elongated striker bar having top and bottom surfaces and a front flat impact surface therebetween, the bar- having wall surfaces defining a recess in at least one end thereof and opening the rough the end and through the top and bottom surfaces. A generally T-shaped member is provided at one end of the striker bar for mounting the bar in the printer, the leg of the T-shaped member being received in the recess in one end of the bar and having-wall surfaces spaced from an out of contact with the wall surfaces of the striker recess, the member also having an end face in spaced opposition to an end face on the striker bar end. Elastomeric dampening material is disposed between the wall surfaces of the leg and the recess and between the end faces of the member and striker bar, respectively.
In a further preferred embodiment according to the present invention, there is provided a method of fabricating a striker bar assembly for an impact printer comprising forming endwise opening recesses at each of the opposite ends of a striker bar body, providing a pair of mounting members each including an element projecting therefrom for reception in the recess, dimensioning each element and recess to provide a gap between the element and the wall surfaces defining the recess when the element is disposed in the recess, disposing the elements in the corresponding recesses at opposite ends of the striker bar body and disposing an elastomeric material in the gap such that the elements and the striker bar body are secured one to the other and out of direct contact with one another.
Accordingly, it is a primary object of the present invention to provide a novel and improved striker bar assembly and methods of manufacturing the assembly which enable direct replacement of the striker bar assembly without further adjustment, afford little or no impact on print quality as a result of dampening motion and enable a molding configuration that equalizes molded-in-stresses to virtually eliminate shrinkage of the dampening material in a front-to-back direction.